Cathode, lithium air battery including same, and preparation method thereof

ABSTRACT

An air battery cathode including an organic-inorganic composite material including lyophobic nanopores, the organic-inorganic composite material including a porous metal oxide, and a lyophobic layer on a surface of a pore of the porous metal oxide and having a contact angle of greater than about 90°; and a binder. Also a lithium air battery including the cathode, and a method of manufacture the cathode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2013-0018830, filed on Feb. 21, 2013, and all thebenefits accruing therefrom under 35 U.S.C. §119, the content of whichis incorporated herein in its entirety by reference.

BACKGROUND

1. Field

The present disclosure relates to a cathode, a lithium air batteryincluding the same, and preparation methods thereof.

2. Description of the Related Art

A lithium air battery includes an anode capable of intercalating anddeintercalating lithium, a cathode that oxidizes or reduces oxygen inthe air, and an electrolyte disposed between the anode and the cathode.

Since the lithium air battery uses lithium metal as an anode and doesnot have to store the cathode active material (i.e., oxygen in the air)within the battery, the lithium air battery may have high capacity. Alithium air battery has a high theoretical energy density per unitweight of 3,500 Watt-hours per kilogram (Wh/kg) or greater, which isabout ten times greater than that of a lithium ion battery.

It has been disclosed that a concentration gradient of oxygen occurswithin a porous cathode, and that the concentration of oxygen isdecreased in an area adjacent to a separator. Thus, due to the lowconcentration of oxygen in the area adjacent to the separator, adischarge capacity of the cathode may be limited. In order to increasethe concentration of oxygen that is delivered to the inside of thecathode, a porosity of the cathode may be increased. However, in regardto the cathode having improved porosity, impregnation of the electrolyteis increased, and accordingly oxygen delivery may be blocked.

Therefore, there is a demand for methods of improving the dischargecapacity of the lithium air battery by increasing the concentration ofthe cathode active material without increasing impregnation of theelectrolyte within the cathode.

SUMMARY

Provided is a cathode including a novel organic-inorganic compositematerial.

Provided is a lithium air battery including the cathode.

Provided are methods of manufacturing the composite material.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description.

According to an aspect, an air battery cathode includes anorganic-inorganic composite material having lyophobic nanopores, theorganic-inorganic composite material including a porous material, and alyophobic layer on a surface of a nanopore of the porous material; and abinder.

According to another aspect, a lithium air battery includes an anodecapable of absorbing and desorbing lithium ions; the air batterycathode; and an electrolyte disposed between the cathode and the anode.

According to another aspect, a method of manufacturing an air batterycathode includes combining an organic-inorganic composite material and abinder to manufacture the cathode, wherein the organic-inorganiccomposite material is manufactured by: impregnating a porous materialwith a reactive compound including a reactive functional group bondableto the porous material; and chemically bonding the reactive compound toa surface of the porous material to form a lyophobic layer on thesurface of the porous material to manufacture the organic-inorganiccomposite material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic view of a structure of an embodiment of a lithiumair battery;

FIGS. 2A to 2C are high resolution transmission electron microscopy(“HR-TEM”) images of porous silica used in the manufacturing ofcomposite materials in Example 1;

FIG. 3 is a schematic view illustrating an embodiment of a reaction forformation of chemical bonds on a porous surface;

FIG. 4 is a schematic view illustrating a method of measuring a contactangle;

FIG. 5 is a graph of incremental pore volume (cubic centimeters pergram, cm³/g) versus pore diameter (nanometers, m) illustrating a poredistribution of the materials prepared according to Example 1 andComparative Example 1; and

FIG. 6 is a graph of voltage (volts, V) versus specific capacity(milliampere-hours per gram, mAh/g) illustrating a first charge anddischarge cycle of lithium air batteries prepared according to Examples7 to 9 and Comparative Example 9.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of a cathode, alithium air battery including the cathode, and a preparation methodthereof, examples of which are illustrated in the accompanying drawings,wherein like reference numerals refer to like elements throughout. Inthis regard, the present embodiments may have different forms and shouldnot be construed as being limited to the descriptions set forth herein.Accordingly, the embodiments are merely described below, by referring tothe figures, to explain aspects of the present description. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. “Or” means “and/or.” Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes,” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

“Alkoxy” means an alkyl group that is linked via an oxygen (i.e.,—O-alkyl). Nonlimiting examples of C1 to C30 alkoxy groups includemethoxy groups, ethoxy groups, propoxy groups, isobutyloxy groups,sec-butyloxy groups, pentyloxy groups, iso-amyloxy groups, and hexyloxygroups.

“Alkyl” means a straight or branched chain saturated aliphatichydrocarbon having the specified number of carbon atoms, specifically 1to 12 carbon atoms, more specifically 1 to 6 carbon atoms. Alkyl groupsinclude, for example, groups having from 1 to 50 carbon atoms (C1 to C50alkyl).

A cathode according to an embodiment includes an organic-inorganiccomposite material having lyophobic nanopores; and a binder, whereinoxygen is used as a cathode active material.

The lithium air battery may use an aqueous electrolyte and/or an organicnon-aqueous electrolyte as an electrolyte. When the organic non-aqueouselectrolyte is used, a reaction mechanism of a lithium air battery maybe represented by the following Reaction Scheme 1:4Li+O₂

2Li₂O E^(o)=2.91 V2Li+O₂

Li₂O₂ E^(o)=3.10 V  Reaction Scheme 1

During discharge, a lithium ion originated from the anode reacts withoxygen introduced from the cathode to form a lithium oxide, and as aresult, the oxygen is reduced (referred to as an “oxygen reductionreaction (‘ORR’)”). During charge, the lithium oxide is reduced andoxygen is generated as a result of oxidizing of the oxygen (referred toas an “oxygen evolution reaction (‘OER’)”). Also, during discharge,Li₂O₂ is deposited on the pores of the cathode, and a capacity of thelithium air battery increases as a concentration of oxygen diffused intothe cathode increases.

According to an embodiment, the cathode includes the organic-inorganiccomposite material having lyophobic nanopores. Oxygen may be more easilydelivered throughout, e.g., to the inside of, the cathode through thelyophobic nanopores and a passage for oxygen delivery may be maintainedsince the lyophobic nanopores are not impregnated by the electrolyte.Thus, oxygen transport in the cathode may be improved. As a result, andwhile not wanting to be bound by theory, by maintaining a higherconcentration of oxygen inside the cathode, the discharge capacity ofthe lithium air battery including the cathode may be increased.

The nanopores included in the organic-inorganic composite material maybe nano-sized pores and each may have a diameter of less than 1,000 nm.The composite material may have an ordered pore structure. For example,the composite material may have an ordered pore structure having aplurality of regularly arranged pores as shown in FIG. 2B. The orderedpore structure may provide a continuous and/or linear passage withoutcurves, and thus oxygen may be more easily delivered within andthroughout the cathode. Also, a material having an irregular porestructure may contain pores having variously sized cross sections, andthe pores may be connected to each other through a narrower space thanthe pores themselves. Thus, in a material having a discontinuous and/orsinuous passage that is provided by pores having the irregular porestructure, the delivery of oxygen may be inhibited or effectivelyprevented.

The organic-inorganic composite material included in the cathode maycomprise a porous metal oxide, and the organic-inorganic compositematerial may have a number of channels through which oxygen may bedelivered.

In addition, the composite material may have a periodic pore structure.For example, the composite material may have a periodic arrangement ofpores having a cubic, lamellar, oblique, centered rectangular,body-centered orthorhombic, body-centered tetragonal, rhombohedral, orhexagonal topology or architecture. In some embodiments, the compositematerial may have a periodic arrangement of pores as shown in FIG. 2C.

The pores included in the composite material may each have a size of 3nm or greater, for example, in a range from about 3 nm to about 50 nm.In some embodiments, the size may be in a range from about 3.5 nm toabout 15 nm, or from about 5 nm to about 15 nm. When the size is lessthan 2 nm, oxygen may not be easily delivered through the pores, andwhen the size is greater than 50 nm, a mechanical strength to maintain abackbone of the composite material may not be obtained. In anembodiment, an average pore size of the pores in the composite materialmay be about 3 nm to about 50 nm, specifically about 3.5 nm to about 30nm, more specifically about 5 nm to about 15 nm.

In some embodiments, a maximum peak in a pore size distribution of thecomposite material, when obtained by a Barrett-Joyner-Halenda (“BJH”)method, may be in a range from about 3 nm to about 50 nm. For example,the maximum peak in a pore size distribution may be in a range fromabout 3 nm to about 30 nm, when obtained by the BJH method.

The composite material may have pores that are substantially uniform insize. The term “substantially uniform” used herein refers to that 75% ormore, for example, in a range from about 80% to about 95%, of pores havea pore diameter within a range of 30%, for example, within a range of10%, or within a range of 5%, of an average pore diameter. For example,85% or more, for example, in a range from about 90% to about 95%, of thepores included in the composite material may have a pore diameter withina range of 30%, for example, within a range of 10%, or within a range of5%, of the average pore diameter. In an embodiment, a peak in a poresize distribution of the composite material, when obtained by the BJHmethod, is in a range from about 3 nm to about 50 nm, and 75% of thepores have a size of about 3 nm to about 50 nm. In another embodiment, apeak in a pore size distribution of the composite material, whenobtained by the BJH method, is in a range from about 5 nm to about 15nm, and 85% of the pores have a size of about 3 nm to about 50 nm, whenobtained by the BJH method.

The composite material may have a specific surface area of 500 squaremeters per gram (m²/g) or less, when measured using theBrunauer-Emmett-Teller (“BET”) method. In some embodiments, the porouscarbon-based composite material may have a specific surface area in arange from about 100 m²/g to about 500 m²/g. For example, the specificsurface area of the porous carbon-based composite material may be in arange from about 200 m²/g to about 400 m²/g.

The composite material may be in the form of a particle, and in bulk maybe in the form of a powder. Therefore, the composite material may bemolded into various forms, and used for a variety of applications.

In addition, the composite material of the cathode may partially includea lyophobic layer. For example, the cathode may include a layerincluding the composite material, wherein a portion of the layer surfaceis lyophobic. For example, the cathode may have a structure in which thelyophobic layer is disposed in at least a portion of a surface of thecathode. The lyophobic layer may be disposed on a portion, e.g., 10percent (%) to 90%, specifically 20% to 80%, of the lyophobic nanopores.Also, the cathode may include a partially lyophobic layer, e.g., apartially lyophobic layer formed by combining the lyophobic compositematerial with a lyophilic material.

In the cathode, the composite material may include a porous metal oxide;and a lyophobic coating layer that is disposed, e.g., formed, on atleast a portion of the pores included in the porous metal oxide. Thecomposite material may be porous.

By forming the lyophobic coating layer as described above, the compositematerial may become lyophobic, and the lyophobic coating layer may bedisposed uniformly on an inside thereof and on an outer surface of theporous metal oxide.

The porous metal oxide may include at least one element of Groups 3 to14 of the Periodic Table of the Elements. For example, the porous metaloxide may include at least one element of Mg, Al, Si, P, Ca, Ti, V, Ga,Ge, Sr, Zr, Nb, Mo, In, Sn, Hf, Ta, or W.

In some embodiments, examples of the porous metal oxide may compriseSiO₂, TiO₂, NiO, PbO₂, CoO₂, Co₃O₄, Mn₂O₃, MnO₂, MnO, GeO₂, BaTiO₃,zeolite, Al₂O₃, ZnO, or the like, or a combination thereof, but is notlimited thereto. Any suitable material available as a porous metal oxidein the art may be used.

In the composite material, the lyophobic coating layer may form achemical bond to the porous metal oxide. In some embodiments, thelyophobic coating layer may include an organic compound which bonds to apore surface of the porous metal oxide. For example, the lyophobiccoating layer may include a monolayer of the organic compound whichbonds to a pore surface of the porous metal oxide. For example, thelyophobic coating layer may include a monolayer of an organic compound,wherein the monolayer is self-assembled on the pore surface of theporous metal oxide. That is, the lyophobic coating layer may be asurface modifier that modifies the surface characteristics of the poresurface of the porous metal oxide so that the pore is hydrophobic and/orlyophobic. For example, as shown in FIG. 3, the organic compound mayform a chemical bond to the surface of a pore of the porous metal oxideby bonding to functional groups presents on the pore surface. Also, theorganic compound forming the lyophobic coating layer may be disposed ina direction perpendicular to the pore surface. Thus, depending on alength of the organic compound, a thickness of the lyophobic coatinglayer may be selected, e.g., to be about 1 nm to about 20 nm. Forexample, when the length of a linear organic compound 1 is about 1 nm,the thickness of the lyophobic coating layer also may be about 1 nm.

In the composite material, a contact angle of the lyophobic coatinglayer with respect to water at a temperature of 20° C. may exceed about90°, and for example, the contact angle may exceed about 100° or about110°, and may be about 90° to about 170°, or about 95° to about 160°, orabout 100° to about 150°. The contact angle is an angle at a point wherethe surface of water on the lyophobic coating layer is in contact withthe surface of the lyophobic coating layer. For example, the contactangle may correspond to the angle θ in FIG. 4, wherein γ_(SL) is aninterfacial tension between the lyophobic coating layer and water,γ_(sv) is an interfacial tension between the lyophobic coating layer andair, and γ_(Lv) is an interfacial tension between water and air.

The lyophobic coating layer of the composite material may comprise atleast one atom of F, Cl, Br, or I. For example, the lyophobic coatinglayer may include an F atom, and accordingly lyophobicity of thelyophobic coating layer may be improved. In addition, the lyophobiccoating layer may include silicon atoms or oxygen atoms. For example,the lyophobic coating layer may be bonded on the pore surface of theporous metal oxide via an —O—Si— bond.

In the composite material, the thickness of the lyophobic coating layermay be in a range from about 0.1 nm to about 20 nm, but is not limitedthereto. The thickness thereof may be selected depending on the size ofthe organic compound used to form the lyophobic coating layer. Forexample, the thickness of the lyophobic coating layer in the compositematerial may be in a range from about 0.5 nm to about 10 nm. In someembodiments, the thickness thereof may be in a range from about 0.5 nmto about 5 nm, or from about 0.5 nm to about 2 nm.

An amount of the lyophobic coating layer may be about 2 wt % to about 50wt %, specifically about 4 wt % to about 40 wt %, more specificallyabout 6 wt % to about 30 wt %, based on a total weight of theorganic-inorganic composite material.

An amount of the composite material may be in a range from about 1weight percent (wt %) to about 20 wt %, based on a total weight of thecathode. For example, the amount of the composite material may be in arange from about 1 wt % to about 15 wt %, or from about 2 wt % to about10 wt %, based on a total weight of the cathode. When the amount of thecomposite material is too small, the oxygen transfer effect may benegligible. On the contrary, when the amount is too large, the electrontransport may be impeded.

The cathode may additionally include an oxygen oxidation/reductioncatalyst. For example, the catalyst may include at least one of a metalparticle, a metal oxide particle, an organometallic compound, or acombination thereof.

The metal particle may include at least one of Co, Ni, Fe, Au, Ag, Pt,Ru, Rh, Os, Ir, Pd, an alloy thereof, or a combination thereof. Themetal oxide particle may include at least one of manganese oxide, cobaltoxide, iron oxide, zinc oxide, nickel oxide, strontium oxide, lanthanumoxide, barium oxide, lithium oxide, titanium oxide, potassium oxide,magnesium oxide, calcium oxide, yttrium oxide, niobium oxide, zirconiumoxide, copper oxide, chromium oxide, molybdenum oxide, a metal oxidehaving perovskite crystal structure having an empirical formula of AMO₃such as (Sm,Sr)CoO₃, (La,Sr)MnO₃, (La,Sr)CoO₃, (La,Sr)(Fe,Co)O₃,(La,Sr)(Fe,Co,Ni)O₃, La_(0.8)Sr_(0.2)MnO₃ (“LSM”), orLa_(0.6)Sr_(0.4)Co_(0.8)Fe_(0.2)O₃ (“LSCF”), a composite oxide thereof,or a combination thereof. The organometallic compound may include anaromatic heterocyclic compound that is coordinated to a transitionmetal, but is not limited thereto. Any suitable material available as anoxygen oxidation or reduction catalyst in the art may be used.

In some embodiments, the oxygen oxidation or reduction catalyst mayinclude tungsten carbide (WC), a WC fused cobalt, CoWO₄, FeWO₄, NiS,WS₂, La₂O, Ag₂O, cobalt phthalocyanine, or the like, or a combinationthereof.

In addition, the oxygen oxidation and/or reduction catalyst may besupported on a support. The support may be the above-described porouscomposite material, carbon, or the like. Examples of the carbon includecarbon black, such as Ketjen black, acetylene black, channel black, orlamp black, graphite such as natural graphite, artificial graphite, orexpanded graphite, activated carbon, or carbon fiber, but the carbon isnot limited thereto. Any suitable support material available as asupport in the art may be used.

An example of manufacturing the cathode is as follows.

First, the organic-inorganic composite material and the binder arecombined to provide a mixture, and the mixture is added to anappropriate solvent to prepare a cathode slurry. The cathode slurry maybe coated and then dried on a surface of a current collector, optionallypress-molding the dried coating in order to improve an electrodedensity, thereby preparing a cathode.

The binder may include a thermoplastic resin or a thermosetting resin.Examples of the binder are polyethylene, polypropylene,polytetrafluorethylene (“PTFE”), polyvinylidene difluoride (“PVdF”),styrene-butadiene rubber, a tetrafluoroethylene-perfluoroalkylvinylethercopolymer, a vinylidene fluoride-hexafluoropropylene copolymer, avinylidene fluoride-chlorotrifluoroethylene copolymer, anethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, afluorovinylidene-pentafluoro propylene copolymer, apropylene-tetrafluoroethylene copolymer, anethylene-chlorotrifluoroethylene copolymer, a vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer, a vinylidenefluoride-perfluoromethylvinylether-tetrafluoro ethylene copolymer, or anethylene-acrylic acid copolymer, which may be used alone or incombination, but the binder is not limited thereto. Any suitablematerial available as a binder in the art may be used.

A porous body having a network structure or mesh structure may be usedas a current collector to facilitate diffusion of oxygen. A porous metalplate that is made of stainless steel, nickel, or aluminum may be used,and the material thereof is not limited thereto. Any material availableas a current collector in the art may be used. The current collector maybe coated with an anti-oxidation metal or an alloy coating film toprevent oxidation.

The cathode slurry may additionally include a commercially availableoxygen oxidation/reduction catalyst and a conductive material. Also, thecathode slurry may additionally include a lithium oxide.

Any porous and conductive material may be used as a conductive materialof the cathode slurry, and for example, a porous carbon-based materialmay be used. Examples of the porous carbon-based material are carbonblack, graphite, graphene, activated carbon, carbon fibers, or the like.Also, a metallic conductive material, such as a metal fiber and a metalmesh, may be used. Moreover, a metal powder comprising copper, silver,nickel, aluminum, or the like, or a combination thereof, may be used.Also, an organic conductive material, e.g., including a polyphenylenederivatives, may be used. The above-described conductive materials maybe used alone or in a combination.

According to another embodiment, the lithium air battery includes ananode capable of absorbing, e.g., intercalating or alloying, and capableof desorbing, e.g., deintercalating or dealloying, a lithium ion; thecathode, and an electrolyte disposed between the anode and the cathode.

In regard to the lithium air battery, the discharge capacity per unitweight of the cathode in a first discharge cycle may be 530 mAh/g, basedon a total weight of the composite material, the binder, and thecatalyst, at a voltage greater than about 2.0 V with respect to alithium metal, wherein the first discharge cycle is performed at roomtemperature (20° C.) and at 1 atmosphere (atm) under ambient dry airconditions (dew point −80° C.) by applying a constant current of about 1mA/cm² in a voltage window ranging from about 2.0 V to about 4.2 V.

For example, the discharge capacity may be 550 mAh/g, based on a totalweight of the composite material, the binder, and the catalyst orgreater, or 700 mAh/g, based on a total weight of the compositematerial, the binder, and the catalyst, or greater.

Examples of the anode capable of absorbing and desorbing a lithium ioninclude Li metal, an alloy of Li metal, or a material capable ofintercalating Li, but the anode is not limited thereto. Any materialavailable as an anode capable of absorbing, e.g., intercalating, anddesorbing, e.g., deintercalating, a lithium ion in the art may be used.Since the anode may effectively determine the capacity of the lithiumair battery, the anode may be, for example, a lithium metal. The alloyof the Li metal may be an alloy of lithium and another metal, forexample, aluminum, tin, magnesium, indium, calcium, titanium, orvanadium, or the like, or a combination thereof.

The electrolyte may be an organic non-aqueous electrolyte or an aqueouselectrolyte.

The organic electrolyte may include an aprotic solvent. Examples of theaprotic solvent are carbonate-based, ester-based, ether-based,ketone-based, and alcohol-based solvents. Examples of thecarbonate-based solvents are dimethyl carbonate (“DMC”), diethylcarbonate (“DEC”), ethyl methyl carbonate (“EMC”), dipropyl carbonate(“DPC”), methyl propyl carbonate (“MPC”), ethyl propyl carbonate(“EPC”), methylethyl carbonate (“MEC”), ethylene carbonate (“EC”),propylene carbonate (“PC”), butylene carbonate (“BC”), or tetraethyleneglycol dimethyl ether (“TEGDME”). Examples of the ester-based solventsare methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate,methyl propionate, ethyl propionate, γ-butyrrolactone, decanolide,valerolactone, mevalonolactone, or caprolactone. Examples of theether-based solvents are dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. An exampleof the ketone-based solvent is cyclohexanone. Also, examples of thealcohol-based solvent are ethyl alcohol or isopropyl alcohol. Examplesof the aprotic solvent are not limited thereto, and any suitablecombination of the foregoing, or any suitable material available as anaprotic solvent in the art, may be used.

In addition, examples of the aprotic solvent include nitriles, such ascompounds of the formula R—CN, wherein R is a C₂-C₂₀ linear, branched,or cyclic hydrocarbon-based moiety that may include a double-bondedaromatic ring or an ether bond, amides such as dimethylformamide,dioxolanes such as 1,3-dioxolane, or sulfolanes.

As noted, the aprotic solvent may be used alone or in a combination oftwo or more. In the latter case, a mixing ratio of at least two aproticsolvents may be appropriately selected depending on a performance of thebattery, and the mixing ratio may be determined by one of ordinary skillin the art without undue experimentation.

In addition, the organic electrolyte may include an ionic liquid.Examples of the ionic liquid are compounds consisting of cations such aslinearly or branchedly substituted ammonium, linearly or branchedlysubstituted imidazolium, linearly or branchedly substitutedpyrrolidinium, or linearly or branchedly substituted piperidiniumcations, and anions such as PF₆ ⁻, BF₄ ⁻, CF₃SO₃ ⁻, (CF₃SO₂)₂N⁻,(C₂F₅SO₂)₂N⁻, (C₂F₆SO₂)₂N⁻, and (CN)₂N⁻.

The organic electrolyte may include a salt of an alkali metal and/or analkali earth metal. The salt of the alkali metal and/or alkali earthmetal, dissolved in an organic solvent, may be used as a source ofalkali metal ions and/or alkali earth metal ions in the battery. Forexample, the salt may facilitate migration of the alkali metal ionsand/or alkali earth metal ions between the cathode and the anode.

In some embodiments, cations of the alkali metal salt and/or alkaliearth metal salt may include lithium ions, sodium ions, magnesium ions,potassium ions, calcium ions, rubidium ions, strontium ions, cesiumions, barium ions, or the like.

Anions of the alkali metal salt and/or alkali earth metal salt in theorganic electrolyte may include at least one ion of PF₆ ⁻, BF₄ ⁻, SbF₆⁻, AsF₆ ⁻, C₄F₉SO₃ ⁻, ClO₄ ⁻, AlO₂ ⁻, AlCl₄ ⁻, C_(x)F_(2x+1)SO₃ ⁻ (wherex is a natural number from 1 to 100),(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂)N⁻ (where x and y are naturalnumbers from 1 to 100), or a halide.

In some embodiments, the salt of the alkali metal and/or alkali earthmetal may include at least one of LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiN(SO₂C₂F₆)₂, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (where x and y are naturalnumbers), LiF, LiBr, LiCl, LiI, or LiB(C₂O₄)₂ (lithium bis(oxalato)borate, “LiBOB”), and examples thereof are not limited thereto. Anysuitable material available as a salt of an alkali metal and/or alkaliearth metal in the art may be used.

In the organic electrolyte, an amount of the salt of the alkali metaland/or alkali earth metal may be in a range from about 100 millimolar(mM) to about 10 molar (M), for example, from about 500 mM to about 2 M.However, an amount of the salt of the alkali metal and/or alkali earthmetal is not particularly limited thereto, as long as the organicelectrolyte may effectively transfer lithium ions and/or electronsduring charging and discharging.

The separator is not limited so long as a composition thereof issuitably durable in an operating environment of the lithium air battery,and examples of the composition are a non-woven polymer such as anon-woven fabric of a polypropylene material or a non-woven fabric of apolyphenylene sulfide material, a porous film of an olefin-based resinsuch as polyethylene, polypropylene, or the like, or a combinationthereof.

Also, a lithium ion conductive solid electrolyte membrane may beadditionally disposed between the anode and the organic electrolyte. Thelithium ion conductive solid electrolyte may serve as a protective layerthat protects lithium contained in the anode from directly reacting withthe impurities, such as water, oxygen or the like, which may be includedin the liquid electrolyte. Examples of the lithium ion conductive solidmembrane are a lithium ion conductive glass, a crystalline lithium ionconductor (e.g., a ceramic or a glass-ceramic), or an inorganic materialcomprising a combination thereof. However, the lithium ion conductivesolid membrane is not limited thereto, and any suitable materialavailable as a lithium ion conductive solid membrane in the art may beused. Also, when a chemical stability of the solid electrolyte membraneis taken into consideration, an example of the lithium ion conductivesolid electrolyte membrane may be an oxide.

An example of the crystalline lithium ion conductor may beLi_(1+x+y)(Al, Ga)_(x)(Ti_(z)Ge_(1-z))_(1-x)Si_(y)P_(3-y)O₁₂, wherein0≤x≤1, and 0≤y≤1, and for example, 0≤x≤0.4, 0<y≤0.6, or 0.1≤x≤0.3,0.1<y≤0.4, and wherein 0≤z≤1. Examples of the lithium ion conductiveglass-ceramic are lithium-aluminum-germanium-phosphate (“LAGP”),lithium-aluminum-titanium-phosphate (“LATP”),lithium-aluminum-titanium-silicon-phosphate (“LATSP”), or the like. Acombination comprising at least one of the foregoing can be used.

The lithium ion conductive solid membrane may further include a polymersolid electrolyte component, in addition to a glass-ceramic component.The polymer solid electrolyte may be a polyethylene oxide doped with alithium salt, and examples of the lithium salt are LiN(SO₂CF₂CF₃₎₂,LiBF₄, LiPF₆, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃, LiN(SO₂CF₃₎₂,LiN(SO₂C₂F₅₎₂, LiC(SO₂CF₃₎₃, LiN(SO₃CF₃₎₂, LiC₄F₉SO₃, LiAlCl₄, or thelike. A combination comprising at least one of the foregoing can beused.

The lithium ion conductive solid electrolyte membrane may furtherinclude an inorganic solid electrolyte component, in addition to theglass-ceramic component. Examples of the inorganic solid electrolytecomponent are Cu₃N, Li₃N, lithium oxynitride phosphorous (LiPON), or thelike. A combination comprising at least one of the foregoing can beused.

An example of manufacturing the lithium air battery is as follows.

First, a cathode including the porous composite material, an anodecapable of intercalating and deintercalating lithium ions, and aseparator are prepared.

Next, the anode is disposed in one side of a case, and the cathode withthe separator is disposed in the other side of the case and opposite tothe anode. Subsequently, an electrolyte is disposed, e.g., injected,between the cathode and the anode, a porous current collector isdisposed on the cathode, and a pressing member that allows air to reachthe cathode is pressed to fix a cell, thereby completing the manufactureof the lithium air battery. A lithium ion conductive solid electrolytemembrane may be further disposed on a surface of the anode.

The case may be divided into upper and lower parts, which contact theanode and cathode, respectively. An insulating resin may be interposedbetween the upper and lower parts to electrically insulate the cathodeand the anode from each other.

The lithium air battery is available either as a lithium primary batteryor a lithium secondary battery. The lithium air battery may have any ofvarious forms, and for example, may be in the form of a coin, a button,a sheet, a stack, a cylinder, a plane, or a horn. Also, the lithium airbattery may be used to provide a large battery for an electric vehicle.

FIG. 1 is a schematic view of an embodiment of a lithium air battery 10.The lithium air battery 10 includes a cathode 15, which is configured touse oxygen as an active material and is disposed adjacent to a firstcurrent collector 14, an anode 13 including lithium and disposedadjacent to a second current collector 12, an organic electrolyte (notillustrated) disposed between the cathode 15 and the anode 13, and aseparator 16 disposed on one surface of the cathode 15. On one surfaceof the anode 13, the separator 21, which is impregnated with the organicelectrolyte, and a lithium ion conductive solid membrane 22 may besequentially disposed. The anode 13, the separator 21, and the solidelectrolyte membrane 22 may be covered with a pouch 23, which contactsthe separator 16. The first current collector 14, which is porous, mayserve as a gas diffusion layer allowing diffusion of air. A pressingmember (not illustrated) allowing air to reach the cathode may befurther disposed on the first current collector 14. A case (notillustrated) of an insulating material is disposed between the cathode15 and the anode to electrically separate the cathode and the anode. Thelithium air battery may be disposed in a stainless steel container ifdesired.

The term “air” used herein is not limited to atmospheric air, and mayrefer to a combination of gases including oxygen, or pure oxygen gas.This broad definition of “air” also applies to other terms, including anair battery, air electrode, or the like.

In some embodiments, a method of manufacturing the organic-inorganiccomposite material includes impregnating a porous metal oxide with areactive compound; and forming a lyophobic coating layer by chemicallybinding the reactive compound onto a pore surface of the porous metaloxide.

By forming a lyophobic coating layer by chemically binding the reactivecompound on a pore surface of the porous metal oxide, theorganic-inorganic composite material is obtained.

The method of impregnating the porous metal oxide with the reactivecompound is performed by contacting, e.g., mixing, the porous metaloxide and the reactive compound. The reactive compound may be used in astate in which it is dissolved in a solvent.

Examples of the porous metal oxide are SiO₂, TiO₂, NiO, PbO₂, CoO₂,MnO₂, MnO, Co₃O₄, Mn₂O₃, GeO₂, BaTiO₃, zeolite, Al₂O₃, ZnO, or the like,but are not limited thereto. Any suitable material available as a porousmetal oxide in the art may be used.

The pore size of the porous metal oxide, e.g., average pore size, may bein a range from about 4 nm to about 50 nm. In some embodiments, the poresize, e.g., average pore size, may be in a range from about 4.5 nm toabout 15 nm, or from about 5 nm to about 11 nm. In some otherembodiments, example, the pore size, e.g., average pore size, may be ina range from about 12 nm to about 13 nm. When the pore size is less than4 nm, the pore may be blocked by the lyophobic coating layer. Also, whenthe pore size is larger than 50 nm, a sufficient mechanical strength tomaintain a backbone of the composite material may not be obtained.

In the manufacturing method, the process of forming the lyophobiccoating layer may be performed at a temperature of 40° C. or higher. Insome embodiments, the process of forming the lyophobic coating layer maybe performed at a temperature in a range from about 40° C. to about 80°C. When the process of forming the lyophobic coating layer is performedat a low temperature, e.g., near 20° C., the reactive compound may notchemically bind onto a surface of the porous metal oxide, and may remainas a residue on the surface of the pores. Then, the residual reactivecompound may be removed in a subsequent drying process. For example, theprocess of forming lyophobic coating layer may be performed by leaving amixture of the reactive compound impregnated on the porous metal oxidecompound at a temperature of 40° C. or higher for about 1 hour.

During the process of forming the lyophobic coating layer, a temperatureof 40° C. or higher may be maintained for about 1 to 10 hours, but isnot limited thereto. Any suitable duration of time available to form thelyophobic coating layer may be used. For example, during the process offorming the lyophobic coating layer, a temperature of 40° C. or highermay be maintained for about 4 to 8 hours.

The process of forming the lyophobic coating layer may be performed in aclosed space, e.g., in a sealed reactor vessel. When the process offorming the lyophobic layer is performed in an open space, the coatinglayer may not be uniformly formed due to volatilization of the solvent,or the like.

The reactive compound used in the method may be dissolved in anon-aqueous solvent. When the reactive compound is dissolved in anaqueous solvent, the reactive compound may be transformed into othercompounds by hydrolysis or the like, and thus may not suitably reactwith the porous metal oxide.

Examples of the non-aqueous solvent are acetone, a ketone, or the like,but are limited thereto. Any suitable material available as a solventthat does not cause hydrolysis in the art may be used. The non-aqueoussolvent may be any suitable aprotic solvent. Aprotic solvents arefurther disclosed above and not repeated for clarity.

After the process of forming the lyophobic coating layer, a dryingprocess that is performed at a temperature in a range from about 10° C.to 150° C. may be further included. A portion of the reactive compoundthat is not reacted, e.g., bonded to the porous metal oxide, or thesolvent, may be removed by the drying process.

In greater detail, the drying process may be performed at a roomtemperature of about 20° C. for about 1 to 3 days, at a temperature in arange from about 70° C. to about 90° C. for about 1 to 2 days, and at atemperature in a range from about 100° C. to about 150° C. for about 1to 4 hours.

The reactive compound may include a reactive functional group that isable to bind to the pore surface of the metal oxide. The reactivefunctional group may include at least one of a hydroxyl group (HO—), athiol group (—SH), an alkoxy group (RO—), a thioalkyl group (RS—), ahalogen group (X—), an aldehyde group (—C(O)H), a carboxyl group(—C(O)OH), or a carboxylate group (—COO), but is not limited thereto.Any suitable material available as a functional group in the art whichis able to bind to a metal oxide may be used.

The reactive compound may include at least some of the fluorinatedcompound, and thereby improved lyophobicity may be provided on thecoating layer.

For example, the reactive compound may include at least one of asiloxane-based compound in which at least some portion is fluorinated, asilazane-based compound in which at least some portion is fluorinated,an aminosilane-based compound in which at least some portion isfluorinated, or a mercaptosilane-based compound in which at least someportion is fluorinated. The reactive compound is not limited thereto.Any suitable material available as a compound in which at least someportion is fluorinated and that is able to combine with a metal oxide inthe art may be used.

Also, the reactive compound may include at least one of anon-fluorinated siloxane-based compound, a non-fluorinatedsilazane-based compound, a non-fluorinated aminosilane-based compound,and a non-fluorinated mercaptosilane-based compound, but the reactivecompound is not limited thereto. Any material available as a compoundthat is not fluorinated, is able to combine with a metal oxide, and isable to provide a suitably lyophobic coating layer may be used.

Hereinafter, an embodiment will be disclosed in further detail withreference to the following examples. These examples shall not limit thescope of the disclosed embodiments.

EXAMPLES

(Manufacture of Lyophobic Porous Composite Material)

Example 1

1 gram (g) of porous silica SiO₂ (available from S-Chemtech, Korea)having a pore size of 8 nanometers (nm) was added to a solutionincluding 4 mL of hexamethylacetone and 1 milliliter (mL) offluorooctyltrimethoxysilane (CF₃(CF₂)₅CH₂CH₂Si(OCH₃)₃), and the poroussilica was impregnated with the silane-based compound for 15 minuteswhile mixing the solution.

The porous silica SiO₂ in which the silane-based compound is impregnatedwas aged in a closed space at a temperature of 60° C. for 6 hours toform a lyophobic coating layer on pores of the silica.

Next, the porous silica SiO₂ was dried in an open space at a temperatureof 20° C. for 48 hours, and then dried again in an open space at atemperature of 80° C. for 24 hours. Finally, the porous silica SiO₂ wasvacuum dried at a temperature of 120° C. for about 2 hours to prepare acomposite material.

In the composite material, an amount of the lyophobic coating layer,measured by thermogravimetric analysis (“TGA”), was 32.2 weight percent(wt %).

FIGS. 2A to 2C are transmission electron microscopy (“TEM”) images ofthe porous silica used in the manufacture of the composite material. Asshown in the micrographs, the composite material shows substantially thesame, ordered, and periodic porous structure except that the pore sizethereof has been relatively reduced in comparison with the bare poroussilica.

Example 2

A composite material was manufactured in the same manner as in Example1, except that the amount of fluorooctyltrimethoxysilane was changed to0.75 mL.

In the composite material, the amount of the lyophobic coating layer,measured by TGA, was 29.9 wt %.

Example 3

A composite material was manufactured in the same manner as in Example1, except that the amount of fluorooctyltrimethoxysilane was changed to0.5 mL.

In regard to the composite material, the amount of the lyophobic coatinglayer, measured by TGA, was 27.3 wt %.

Comparative Example 1

Porous silica SiO₂ (available from S-Chemtech, Korea) having a pore sizeof 8 nm was used as it is.

Comparative Example 2

A composite material was manufactured in the same manner as in Example1, except that the process of forming the lyophobic layer on pores ofthe silica. The porous silica impregnated with the silane-based compoundin a closed space was dried at a temperature of 60° C. for 6 hours wasomitted.

Comparative Example 3

Porous silica SiO₂ having a pore size of 2.8 nm was manufactured asfollows.

As starting materials, tetraethylorthosilicate (“TEOS”, 98% solutionfrom Aldrich) as a silicon source, cetyltrimethylammonium chloride(“CTACl”, 25% from Aldrich) as a surfactant, and NaOH (Samchun PureChemical) were used. The starting materials were mixed in a ratio of 1mole of TEOS:0.25 mole of Na₂O:0.65 mole of CTACl:62 mole of H₂O to forma mixture. Then, after forming a homogeneous gel by stirring themixture, the gel was heated at a temperature of 95° C. for 4 days toobtain a resulting product. The resulting product was filtered andwashed with water to obtain white powder. The white powder calcined at atemperature of 300° C. to remove the surfactant to prepare the poroussilica.

Comparative Example 4

A composite material was manufactured in the same manner as in Example1, except that porous silica having a pore size of 2.8 nm prepared inComparative Example 3 was used.

In regard to the composite material, the amount of the lyophobic coatinglayer, measured by TGA, was 46.5 wt %.

(Manufacture of Cathode)

Example 4

1 g of Pt/C catalyst (28.4 wt % Pt/Vulcan electrocatalyst, TEC 10V30E,TKK, Japan) and 2.5 wt % of the composite material powder based on thetotal weight of the cathode manufactured according to Example 1 wereadded to a 250 mL polypropylene (“PP”) bottle. 50 milligrams (mg) ofacetone was added thereto, and the mixture was stirred for 5 minutes.Then, the mixture was ultra-sonicated for 15 minutes. Next, 180 g ofdistilled water was added thereto, and stirred for 5 minutes, andcentrifuged at a rate of 8,000 revolutions per minute (“RPM”) for 5minutes. The PP bottle including the centrifuged mixture was added to acontainer containing liquid nitrogen, and the mixture was cooled. Thecooled mixture was freeze-dried for 4 days. The resulting product wasleft in a dryroom to obtain dry powder.

1 g of the dry powder was added to a 250 mL PP bottle, and 3.2 g ofN-methylpyrrolidone was added thereto and stirred in a Thinky AR-500stirrer at a rate of 1,000 RPM for 15 minutes. PVdF was added thereto inan amount to of 2.5 wt % based on the total weight of the cathode, andthe mixture was stirred in the Thinky AR-500 stirrer at a rate of 1,000RPM for 15 minutes to obtain a cathode slurry.

A gas diffusion layer (“GDL”, SGL company, 25BC) was disposed on a glasssubstrate, and the cathode slurry was coated thereon to provide 10mg/cm² based on the weight after drying. Then, the substrate was driedat room temperature in the dryroom for 48 hours and at a temperature of80° C. for 3 hours, and vacuum dried again at a temperature of 120° C.for 2 hours. The substrate was left in the dryroom to obtain a cathode.

A portion of the cathode was cut in the shape of a circle having adiameter of 8 mm and separated from the glass substrate to be used tomanufacture a battery.

Example 5

A cathode was manufactured in the same manner as in Example 4, exceptthat the composite material powder manufactured according to Example 1was added in an amount of 5.0 wt % based on the total weight of thecathode.

Example 6

A cathode was manufactured in the same manner as in Example 4, exceptthat the composite material powder manufactured according to Example 1was added in an amount of 8.0 wt % based on the total weight of thecathode.

Comparative Examples 5 to 7

A cathode was manufactured in the same manner as in Example 4, exceptthat the composite material powders manufactured according toComparative Examples 1 to 3 were used respectively.

Comparative Example 8

A cathode was manufactured in the same manner as in Example 4, exceptthat the composite material powder manufactured according to ComparativeExample 4 was added in an amount of 5.0 wt % based on the total weightof the cathode.

(Manufacture of Lithium Air Battery)

Example 7

A separator (Celgard 3501) was disposed on a lithium metal thin film.

Then, 400 mL of an electrolyte solution in which 1 M lithiumbis(trifluoromethanesulfonyl)imide (“LiTFSI”) was dissolved in propylenecarbonate (“PC”) was injected into the separator.

A lithium-aluminum titanium phosphate (“LATP”) solid electrolyte film(having a thickness of 250 μm, available from Ohara Corp., Japan) wasdisposed on the separator to prepare a substructure. The substructurewas then covered with a pouch in which aluminum is coated on apolyolefin base. Since a fixed size of a window was provided on theupper side of the pouch, a portion of the solid electrolyte is exposedto the outside. Then, 50 microliters (μL) of an electrolyte solution inwhich 1 M LiTFSI was dissolved in TEGDME was injected to the solidelectrolyte, which was exposed to the outside.

A separator (Celgard 3501) was disposed on the solid electrolyte, whichwas exposed to the outside, and 30 μL of an electrolyte solution inwhich 1 M LiTFSI was dissolved in TEGDME was injected to the separator.

The cathode manufactured according to Example 4 was disposed on theseparator. Then, a stainless steel mesh was disposed on the cathode. Thecathode was pressed and fixed by a pressing member disposed on thecathode to manufacture a lithium air battery. Air is able to passthrough the pressing member and reach the cathode.

Examples 8 and 9

A lithium air battery was manufactured in the same manner as in Example7, except that the cathodes manufactured according to Examples 5 and 6were used respectively.

Comparative Examples 9 to 12

A lithium air battery was manufactured in the same manner as in Example7, except that the cathodes manufactured according to ComparativeExamples 5 and 8 were used respectively.

Evaluation Example 1: Lyophobicity Evaluation

The materials manufactured in Examples 1 to 3 and Comparative Examples 1to 4 were impregnated with an electrolyte solution in which 1M LiTFSIwas dissolved in TEGDME, and a color change was observed.

Lyophilic materials were completely impregnated with electrolytesolution by wetting with the electrolyte solution, and becametransparent immediately or in a few seconds. The lyophobic material isnot wetted by the electrolyte solution, or may be slightly wetted, andthus it may maintain a white color for at least one minute after beingimpregnated in the electrolyte solution.

The composite materials of Examples 1 to 3 show that the lyophobic layerwas formed since they maintained a white color for 1 minute.

Also, the composite materials of Comparative Examples 1 to 3 becametransparent immediately, the composite material of Comparative Example 2became transparent after 2 or 3 seconds, and the composite material ofComparative Example 4 maintained a white color for more than 1 minute.

Comparative Example 2: Porosity Evaluation

In the materials manufactured according to Examples 1 to 3 andComparative Examples 1 to 4, a BET specific surface area and pore sizedistribution (4V/A by BET) were measured by using the BET andBarrett-Joyner-Halenda (“BJH”) methods, respectively. Evaluation ofmicropores and an external surface area was performed by using a t-plotmethod. Some results are shown in Table 1 below.

TABLE 1 Average pore size BET specific surface area (4 V/A by BET)[m²/g] [nm] Example 1 315.6 8.11 Comparative Example 1 601.6 9.22Comparative Example 3 1084 2.8  Comparative Example 4 473 Unable tomeasure

As shown in Table 1 above, the composite material in which the lyophobiccoating layer of Example 1 was formed has a reduced specific surfacearea as compared to the porous silica of Comparative Example 1 that doesnot have the lyophobic coating layer.

Also, as shown in FIG. 5, a size of pores having the maximum volume isdecreased by about 2 nm in the pore size distribution of Example 1 ascompared to Comparative Example 1. Thus, it was confirmed that alyophobic coating layer having a thickness of about 1 nm was formed on apore surface of the porous silica.

In addition, since the average pore size is decreased by about 2 nm andthe length of fluorooctyltrimethoxysilane forming the lyophobic coatinglayer is about 1 nm, the fluorooctyltrimethoxysilane may be bondedvertically on a pore surface or self-assembled.

A peak was not observed in the pore size distribution of ComparativeExample 4 (not shown), and thus it is not substantially possible tomeasure the average pore size. While not wanting to be bound by theory,it is understood that the pores in Comparative Example 4 are mostlysubstantially clogged.

Evaluation Example 3: Evaluation of Charge and Discharge Characteristics

At a temperature of 60° C. and in a 1 atmosphere (atm) oxygenatmosphere, a charge and discharge cycle was performed in such a waythat the lithium air batteries manufactured in Examples 7 to 9 andComparative Examples 9 to 12 were each discharged to 2.0 volts (V) (vs.Li) with a constant current of 1 mA/cm², and then charged again to 4.2 Vwith the same current. Some results of a first cycle of a charge anddischarge test are shown in Table 2 below and in FIG. 3.

The specific capacity is determined based on a total weight of a cathodeincluding a composite material, a catalyst, and a binder.

TABLE 2 Discharge specific capacity [mAh/g] Comparative 541 Example 9Comparative 532 Example 12 Example 7 535 Example 8 828 Example 9 713

As shown in Table 2 above, the lithium air batteries of Examples 7 to 9have increased discharge capacity despite relatively lower BET specificsurface area values compared to that of Comparative Example 9. Thedischarge capacity of the lithium air batteries of Examples 8 and 9 aresignificantly increased.

The increase in the discharge capacity may be due to an increase inoxygen delivery to the inside of the cathode and accordingly by anincrease in oxygen concentration inside the cathode.

Also, according to another aspect, the discharge capacity of the lithiumair battery may be increased by including the novel organic-inorganiccomposite material.

It should be understood that the exemplary embodiments disclosed hereinshall be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features, advantages, or aspects within eachembodiment should be considered as available for other similar features,advantages, or aspects in other embodiments.

What is claimed is:
 1. An air battery cathode comprising: anorganic-inorganic composite material comprising surface modifiednanopores, the organic-inorganic composite material comprising a porousmaterial, wherein the porous material is a porous metal oxide, and asurface modifier on a surface of a nanopore of the porous material; anda binder.
 2. The cathode of claim 1, wherein the pores of the porousmaterial are ordered.
 3. The cathode of claim 1, wherein the pores ofthe porous material have a periodic pore structure, and a contact anglebetween a surface of the organic-inorganic composite material and wateris greater than about 90°, wherein the contact angle is determined usingwater and at a temperature of 20° C.
 4. The cathode of claim 1, whereinthe composite material has an average pore size in a range from about 3nanometers to about 50 nanometers.
 5. The cathode of claim 4, whereinthe composite material has a peak in a pore size distribution of thecomposite material in a range from about 3 nanometers to about 50nanometers, and 75% of the pores have a size of about 3 nanometers toabout 50 nanometers.
 6. The cathode of claim 4, wherein an amount of thesurface modifier may be about 2 weight percent to about 50 weightpercent, based on a total weight ofthe organic-inorganic compositematerial.
 7. The cathode of claim 1, wherein the composite material hasan average pore size in a range from about 3 nanometers to about 15nanometers.
 8. The cathode of claim 1, wherein the composite material isin a form of particles.
 9. The cathode of claim 1, wherein the surfacemodifier is disposed on at least a portion of the surface of thenanopore of the porous metal oxide.
 10. The cathode of claim 9, whereinthe metal oxide comprises at least one element of Groups 3 to 14 of thePeriodic Table.
 11. The cathode of claim 9, wherein the metal oxidecomprises at least one of Mg, Al, Si, P, Ca, Ti, V, Ga, Ge, Sr, Zr, Nb,Mo, In, Sn, Hf, Ta, or W.
 12. The cathode of claim 9, wherein thesurface modifier is chemically bonded to the porous metal oxide.
 13. Thecathode of claim 9, wherein the surface modifier comprises an organiccompound which is bonded to the surface of the pores of the porous metaloxide.
 14. The cathode of claim 1, wherein the surface modifiercomprises F, Cl, Br, I, or a combination comprising at least one of theforegoing.
 15. The cathode of claim 1, wherein the surface modifiercomprises silicon.
 16. The cathode of claim 1, wherein the surfacemodifier has a thickness in a range from about 0.1 nanometers to about20 nanometers.
 17. The cathode of claim 1, wherein the compositematerial is contained in an amount in a range from about 1 weightpercent to about 20 weight percent, based on a total weight of thecathode.
 18. A lithium air battery comprising: an anode capable ofabsorbing and desorbing lithium ions; the air battery cathode accordingto claim 1; and an electrolyte disposed between the anode and thecathode.
 19. The cathode of claim 1, wherein, when contacted with anelectrolyte, the surface modifier is not impregnated by the electrolyte.20. The cathode of claim 1, wherein the porous metal oxide comprisesSiO₂, TiO₂, NiO, PbO₂, CoO₂, Co₃O₄, Mn₂O₃, MnO₂, MnO, GeO₂, BaTiO₃,zeolite, Al₂O₃, ZnO, or a combination thereof.
 21. The cathode of claim1, wherein a contact angle between a surface of the organic-inorganiccomposite material and water is greater than about 90°, wherein thecontact angle is determined using water and at a temperature of 20° C.